1. Field of the Invention
The present invention relates to a printed circuit board for electrical devices having RF components, particularly for mobile radio telecommunication devices, wherein the printed circuit board has a xe2x80x9cmicro viaxe2x80x9d coating applied to it and includes RF circuits, non-RF circuits, RF conductor-track structures and non-RF conductor-track structures arranged on it.
2. Description of the Prior Art
In electrical devices having radio-frequency components or radio-frequency device parts (RF component; RF device parts), these RF components need [lacuna] to be separated from the non-RF components (e.g. AF components) or protected against reciprocal influences, on account of interreactions which arise between such components. This may occur because (1) the RF signals affect the AF response of the AF components if the latter are a placed too close to the RF components; (2) or when the AF components are placed too close to the RF components, the RF parameter settings of the RF components are affected. A typical location where RF components (RF circuits with RF interconnections and RF components) and non-RF components (non-RF circuits with non-RF interconnections and non-RF components) are arranged in close proximity to one another is a printed circuit board or electronic printed circuit board assembly in electrical devices. Furthermore, the interfering interaction between the components is accentuated in small electrical devices with small printed circuit boards. On the other hand, the demand for ever smaller and more compact electrical devices is increasing. This is particularly; the case where the miniaturized devices are portable i.e., the user can take them virtually anywhere (to any geographical location). One example of such small portable devices is mobile radio communication devices.
On the basis of the multiplicity of mobile radio telecommunication devices ( such as DECT telecommunication devices, GSM telecommunication devices, PHS telecommunication devices, xe2x80x9cIS-95xe2x80x9d telecommunication devices and other telecommunication devices based on pure or hybrid transmission methods from the basic transmission methods FDMA, TDMA, CDMA (e.g., the DS-CDMA method or the JD-CDMA method) which are used for a variety of message transmission purposes (such as the transmission of speech, packet and/or video data) and which give rise, by way of example, to the problems illustrated above relating to xe2x80x9cdemand for miniaturization on the one hand and avoidance of the interfering interaction between RF components and AF components on the otherxe2x80x9d in the context of the demand for cheaper and cheaper devices (i.e., mass-produced product), the following gives a representative illustration and explanation, for all the devices mentioned, of the effects produced thereby, using the example of a DECT mobile part.
FIG. 1 shows a first printed circuit board LP1, which is used in the Siemens xe2x80x9cGIGASET 1000 S,Cxe2x80x9d DECT mobile part and, for production engineering reasons, is preferably fitted with components on one side. As shown in the cross section illustration in FIG. 2, the printed circuit board LP1 has a multilayer first printed circuit board assembly LPT1 which includes four printed circuit board layers LPL1 . . . LPL4, has a thickness of approx. 1350 xcexcm, and is preferably constructed using the known hybrid masslam process. The printed circuit board assembly LPT1 referred to here contains a first core K1 having a thickness of approx. 360 m, and having with a first metal coating M1K1 (third printed circuit board layer LPL3) which is arranged on the underside of the core K1, is preferably made of copper. The first core K1 also has a second metal coating M2K1 (second printed circuit board layer LPL2) which is arranged on the top of the core K1 and is preferably made of copper. The metal coatings M1K1, M2K1 have a respective first xe2x80x9cprepregxe2x80x9d coating P1, with a thickness of in each case approx. 360 xcexcm, arranged on them. The xe2x80x9cprepregxe2x80x9d coatings denoted are glass fiber reinforced epoxy coatings. The xe2x80x9cprepregxe2x80x9d coating PI arranged on the metal coating M1K1 has, on the side opposite the metal coating M1K1, a third metal coating M1P1 (fourth printed circuit board layer LPL4) which is preferably made of copper and, on the side opposite the metal coating M2K1, a fourth metal coating M2P1 (first printed circuit board layer LPL1) which also is preferably made of copper. The first printed circuit board layer LPL1 has a critical first RF conductor-track structure LBS1RF, for example, arranged in it, whilst the second printed circuit board layer LPL2 is provided with a first non-RF conductortrack structure LBS1NRF and/or a first non-RF circuit interconnection SVD1NRF, for example. To protect the RF conductor-track structure LBSL1RF in relation to the RF ground coating MSRF in the third printed circuit board layer LPL3 from the influence of the non-RF conductor-track structure LBS1NRF and/or a first non-RF circuit interconnection SVD1NRF, the second printed circuit board layer LPL2 is provided with a first barrier area SB1 which largely surrounds first field lines FL1 of the RF signal. Furthermore, the printed circuit board assembly LPT1 has first through holes DB1LPT1 for RF connections and non-RF connections between the first printed circuit board layer LPL1 and the fourth printed circuit board layer LPL4, as well as second through holes DB2LPT1 for connecting external modules (e.g. earpiece, microphone etc.).
FIG. 3 shows an enlarged three-dimensional illustration of the region drawn in dashed lines in FIG. 2.
FIG. 4 shows a second printed circuit board LP2, used in the Siemens xe2x80x9cGIGASET 2000 S,Cxe2x80x9d DECT mobile part and again, for production engineering reasons, preferably fitted with components on one side. As shown in the cross section illustration in FIG. 5, the printed circuit board LP2 has a multilayer second printed circuit board assembly LPT2, which again includes the four printed circuit board layers LPL1 . . . LPL4, has a thickness of approx. 1350 xcexcm, and is preferably constructed using the known hybrid masslam process. The printed circuit board assembly LPT2 referred to here contains a second core K2 having a thickness of approx. 360 xcexcm and having a fifth metal coating M1K2 (third printed circuit board layer LPL3) which is arranged on the underside of the core K2 and is preferably made of copper.
The second core K2 also has a sixth metal coating M2K2 (second printed circuit board layer LPL2) which is arranged on the top of the core K2, is preferably made of copper, and forms the second RF ground coating MS2RF. The metal coating M1K2, M2K2 has a respective second xe2x80x9cprepregxe2x80x9d coating P2, with a thickness of in each case approx. 360 xcexcm, arranged on it. The xe2x80x9cprepregxe2x80x9d coating P2 arranged on the metal coating M1K2 has, on the side opposite the metal coating M1K2, a seventh metal coating M2P2 (fourth printed circuit board layer LPL4) which is preferably made of copper and, on the side opposite the metal coating M2K2, an eighth metal coating M2P2 (first printed circuit board layer LPL1), preferably made of copper. The printed circuit board layers LPL2 . . . LPL4 have a known tri-plate structure arranged in them. This structure includes a critical second RF conductor-track structure LBS2RF in the third printed circuit board layer LPL3, the RF ground coating MS2RF in the second printed circuit board layer LPL2, and a third RF ground coating MS3RF, which is amply designed for second field lines FL2 of the RF signal, in the fourth printed circuit board layer LPL4. Furthermore, the printed circuit board assembly LPT2 has first through holes DB1LPT2 for the RF connections and non-RF connections between the first printed circuit board layer LPL1 and the fourth printed circuit board layer LPL4 as well as second through holes DB2LPT2 for connecting the external modules (e.g. earpiece, microphone etc.).
To reduce the dimensions of the printed circuit boards LP1, LP2 and thusxe2x80x94as explained in the introductionxe2x80x94be able to produce more compact DECT mobile parts, it is known practice to fit components to both sides of the printed circuit boards. This, however, requires higher complexity in terms of production engineering.
When designing printed circuit boards for electrical devices without RF components, it is known practice to use xe2x80x9cmicro viaxe2x80x9d technology (Mv technology) in order to promote the abovementioned miniaturization of electrical devices. In printed circuit technology, xe2x80x9cmicro viasxe2x80x9d denote plated-through holes on printed circuit boards in the order of micrometers. MV technology is an alternative to mechanically plating-through blind holes, which is likewise known. MV technology is a connection technology for cheaply producing printed circuit boards without RF circuits and RF conductor-track structures. The cost saving is achieved by virtue of the fact that not only mechanical drilling operations for blind holes, and the addition and removal of material, but also the deburring of the holes, are dispensed with. A number of production processes for producing such xe2x80x9cmicro viaxe2x80x9d coatings with a large area are currently known. These processes are the xe2x80x9cSequential Built Upxe2x80x9d process (SBU process), the xe2x80x9cSilver Bumpxe2x80x9d process (SB process), the plasma etching process, laser drilling with a CO2 laser and laser drilling with a YAG laser. For large-scale use, the cost aspect (economic viability) means that, from a modern perspective, probably only the first two production processes can be considered. The xe2x80x9cmicro viasxe2x80x9d (plated-through holes) produced using this technology have a diameter of 50 to 150 xcexcm, for example, and require soldering lands, for example, with diameters in the range between 0.12 and 0.35 mm. The xe2x80x9cmicro viaxe2x80x9d diameter is again dependent on the distance between the xe2x80x9cmicro viaxe2x80x9d coating (xe2x80x9cmicro viaxe2x80x9d layer) and the nearest coating (layer) further that have 4 diameter/layer spacing greater than 1. In combination with the very fine conductor technology having conductor-track widths of 50 xcexcm, extremely high wiring densities are achieved.
In the case of standard technologies (e.g., blind-hole plated-through holes) known as an alternative to MV technology, the size of a printed circuit board is determined to a considerable extent by the space requirement for the plated-through holes and by the conductor-track structure on the component side of the printed circuit board. Since it is possible, with MV technology, to xe2x80x9cdip downxe2x80x9d to the first inner layer directly in the xe2x80x9cpadxe2x80x9d of the components, the space requirement for plated-through holes and conductor-track structures is now of only little consequence. As long as RF problems are not an issue, components may be placed as close to one another as is permitted from a production engineering perspective. On the above premise, with MV technology, the printed circuit board size is determined almost exclusively by the number and type of the components used.
The object on which the present invention is based, therefore, is to increase the packing density of electronic circuits and conductor-track structures on printed circuit boards for electrical devices having RF components, particularly for mobile radio telecommunication devices, and hence to reduce the dimensions of the printed circuit board.
The present the invention therefore considers applying a xe2x80x9cmicro viaxe2x80x9d coating to one or both sides of a printed circuit board assembly, applying the device-specific circuits with circuit interconnections and components as well as conductor-track structures (e.g. RF circuits having RF circuit interconnections and RF components as well as RF conductor-track structures or non-RF circuits having non-RF circuit interconnections and non-RF components and non-RF conductor-track structures to at least part of the surface of this xe2x80x9cmicro viaxe2x80x9d coating, and protecting the RF circuits and RF conductor-track structures in relation to an RF ground coating of the printed circuit board assembly by means of barrier areas, or so-called windows, arranged in an assembly layer and situated directly below the xe2x80x9cmicro viaxe2x80x9d coating, of the printed circuit board assembly from interfering influences which impair the RF parameters, to be set in each case, of the RF circuits and RF conductor-track structures (e.g., from the non-RF conductor-track structures and/or non-RF circuit interconnections likewise arranged on the assembly coating, situated directly below the xe2x80x9cmicro viaxe2x80x9d coating, of the printed circuit board assembly).
The procedure described above for constructing a printed circuit board is also valid, or also can be used if (unlike the above embodiments) on the one hand the RF circuit interconnections of the RF circuits and RF conductor-track structures on the assembly coating, situated directly below the xe2x80x9cmicro viaxe2x80x9d coating, of the printed circuit board assembly, and on the other hand the barrier areas and the RF components of the RF circuits, the non-RF conductor-track structures and/or the non-RF circuits with the circuit interconnections. and components, are arranged on the xe2x80x9cmicro viaxe2x80x9d coating. Furthermore, the two procedures may also be combined.
When using xe2x80x9cmicro viaxe2x80x9d technology and the window technique, it must be accepted, for a specific packing volume of circuits and conductor-track structures on the printed circuit board, that the number of printed circuit board layers is increased in comparison with a technology which does not use xe2x80x9cmicro viaxe2x80x9d technology and the window technique. However, the number of printed circuit board layers can be kept unchanged as compared with a technology not using xe2x80x9cmicro viaxe2x80x9d technology and the window technique only if, contrary to the objective on which the present invention is based, the packing density is reduced and, hence, the intended reduction (miniaturization) of the electrical device is not achieved.
If a printed circuit board for electrical devices having RF components, particularly for mobile radio telecommunication devices, is constructed using the proposed method, however, the space required for accommodating the device-specific circuits and conductor-track structures on the printed circuit board is significantly smaller than on printed circuit boards of conventional design.
The rest of the procedure according to an embodiment of the present invention affords the advantage thatxe2x80x94if the distance between the xe2x80x9cmicro viaxe2x80x9d coating and the assembly coating, situated directly below the xe2x80x9cmicro viaxe2x80x9d coating, of the printed circuit board assembly is of the order of magnitude necessary for cheaply producing a xe2x80x9cmicro viaxe2x80x9d coating using the known xe2x80x9cSequential Built Upxe2x80x9d process (SBU process)xe2x80x94in addition to the smaller printed circuit board design on account of the higher packing density, the production costs for the printed circuit board are drastically reduced.
A further development of the present invention allows, for example on the basis of the xe2x80x9chole diameter of a xe2x80x9cmicro viaxe2x80x9d relating to the distance between the xe2x80x9cmicro viaxe2x80x9d coating and the assembly coating, situated directly below the xe2x80x9cmicro viaxe2x80x9d coating, of the xe2x80x9cprinted circuit board assemblyxe2x80x9d condition, with typical hole diameters of between 50 xcexcm and 150 xcexcm, the ratio of the hole diameter to the layer spacing to be greater than 1, and requires soldering land diameters of between 0.12 mm and 0.35 mm.
As a result of another development of the present invention, a further reduction in the size of the printed circuit board design is possible because the RF circuit, which additionally can be applied to the xe2x80x9cmicro viaxe2x80x9d coating covering the first holes (xe2x80x9cstandard viasxe2x80x9d), can be used to increase the packing density further.
Yet another development of the present invention ensures that, when the first holes in the xe2x80x9cmicro viaxe2x80x9d coating are covered, the micro-environment produced in the holes as a result of covering does not cause any blowing (explosion).